* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

*::after,
*::before {
  box-sizing: border-box;

}

#html {
  /*  自动换行 */
  word-break: break-all;
}

#div1 {
  position: fixed;
  top: 50px;
  left: 50%;
  transform: translateX(-50%);
}

#div1::before {
  content: '';
  position: absolute;
}

#div1::after {
  content: '';
  position: absolute;

}

@media(max-width:500px) {
  #html {
    height: 50vh;
    overflow: auto;
  }

  #divWrapper {
    height: 50vh;
  }

  #div1 {
    position: relative;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
  }
}